| Message ID | 20180921150351.20898-21-yu-cheng.yu@intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Control Flow Enforcement: Shadow Stack | expand |
On Fri, Sep 21, 2018 at 08:03:44AM -0700, Yu-cheng Yu wrote: > When setting up a signal, the kernel creates a shadow stack > restore token at the current SHSTK address and then stores the > token's address in the signal frame, right after the FPU state. > Before restoring a signal, the kernel verifies and then uses the > restore token to set the SHSTK pointer. > diff --git a/arch/x86/kernel/cet.c b/arch/x86/kernel/cet.c > index ec256ae27a31..5cc4be6e0982 100644 > --- a/arch/x86/kernel/cet.c > +++ b/arch/x86/kernel/cet.c > @@ -46,6 +47,69 @@ static unsigned long get_shstk_addr(void) > return ptr; > } > > +/* > + * Verify the restore token at the address of 'ssp' is > + * valid and then set shadow stack pointer according to the > + * token. > + */ > +static int verify_rstor_token(bool ia32, unsigned long ssp, > + unsigned long *new_ssp) > +{ > + unsigned long token; > + > + *new_ssp = 0; > + > + if (!IS_ALIGNED(ssp, 8)) > + return -EINVAL; > + > + if (get_user(token, (unsigned long __user *)ssp)) > + return -EFAULT; > + > + /* Is 64-bit mode flag correct? */ > + if (ia32 && (token & 3) != 0) > + return -EINVAL; > + else if ((token & 3) != 1) > + return -EINVAL; It is probably worth adding constant names for these flags, example, there's Section 2.4 in the currently available description[1], and it took some time before I decided to look into other patches and find the patch with the documentation (or finally notice section 2.7). [1] https://software.intel.com/sites/default/files/managed/4d/2a/control-flow-enforcement-technology-preview.pdf > + token &= ~(1UL); > + > + if ((!ia32 && !IS_ALIGNED(token, 8)) || !IS_ALIGNED(token, 4)) > + return -EINVAL; > + > + if ((ALIGN_DOWN(token, 8) - 8) != ssp) > + return -EINVAL; > + > + *new_ssp = token; > + return 0; > +} > + > +/* > + * Create a restore token on the shadow stack. > + * A token is always 8-byte and aligned to 8. > + */ > +static int create_rstor_token(bool ia32, unsigned long ssp, > + unsigned long *new_ssp) > +{ > + unsigned long addr; > + > + *new_ssp = 0; > + > + if ((!ia32 && !IS_ALIGNED(ssp, 8)) || !IS_ALIGNED(ssp, 4)) > + return -EINVAL; Maybe refactor this check into a separate function/macro? > + > + addr = ALIGN_DOWN(ssp, 8) - 8; > + > + /* Is the token for 64-bit? */ > + if (!ia32) > + ssp |= 1; Again, usage of a named constant might document it better. > + > + if (write_user_shstk_64(addr, ssp)) This function is defined in "[RFC PATCH v4 19/27] x86/cet/shstk: Introduce WRUSS instruction" > + return -EFAULT; > + > + *new_ssp = addr; > + return 0; > +} > + > int cet_setup_shstk(void) > { > unsigned long addr, size; > @@ -107,3 +171,54 @@ void cet_disable_free_shstk(struct task_struct *tsk) > > tsk->thread.cet.shstk_enabled = 0; > } > + > +int cet_restore_signal(unsigned long ssp) > +{ > + unsigned long new_ssp; > + int err; > + > + if (!current->thread.cet.shstk_enabled) > + return 0; > + > + err = verify_rstor_token(in_ia32_syscall(), ssp, &new_ssp); > + > + if (err) > + return err; > + > + return set_shstk_ptr(new_ssp); > +} > + > +/* > + * Setup the shadow stack for the signal handler: first, > + * create a restore token to keep track of the current ssp, > + * and then the return address of the signal handler. > + */ > +int cet_setup_signal(bool ia32, unsigned long rstor_addr, > + unsigned long *new_ssp) > +{ > + unsigned long ssp; > + int err; > + > + if (!current->thread.cet.shstk_enabled) > + return 0; > + > + ssp = get_shstk_addr(); > + err = create_rstor_token(ia32, ssp, new_ssp); > + > + if (err) > + return err; > + > + if (ia32) { > + ssp = *new_ssp - sizeof(u32); > + err = write_user_shstk_32(ssp, (unsigned int)rstor_addr); > + } else { > + ssp = *new_ssp - sizeof(u64); > + err = write_user_shstk_64(ssp, rstor_addr); > + } > + > + if (err) > + return err; > + > + set_shstk_ptr(ssp); > + return 0; > +} > diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c > index 92a3b312a53c..e9a85689143f 100644 > --- a/arch/x86/kernel/signal.c > +++ b/arch/x86/kernel/signal.c > @@ -46,6 +46,7 @@ > > #include <asm/sigframe.h> > #include <asm/signal.h> > +#include <asm/cet.h> > > #define COPY(x) do { \ > get_user_ex(regs->x, &sc->x); \ > @@ -152,6 +153,10 @@ static int restore_sigcontext(struct pt_regs *regs, > > err |= fpu__restore_sig(buf, IS_ENABLED(CONFIG_X86_32)); > > +#ifdef CONFIG_X86_64 > + err |= restore_sigcontext_ext(buf); > +#endif > + > force_iret(); > > return err; > @@ -266,6 +271,11 @@ get_sigframe(struct k_sigaction *ka, struct pt_regs *regs, size_t frame_size, > } > > if (fpu->initialized) { > +#ifdef CONFIG_X86_64 > + /* sigcontext extension */ > + if (boot_cpu_has(X86_FEATURE_SHSTK)) > + sp -= sizeof(struct sc_ext) + 8; > +#endif > sp = fpu__alloc_mathframe(sp, IS_ENABLED(CONFIG_X86_32), > &buf_fx, &math_size); That might be refactored in a separate function. Also, it looks like that possible padding for 8-byte alignment (copy_ext_{to,from}_user) is not accounted here. > *fpstate = (void __user *)sp; > @@ -493,6 +503,9 @@ static int __setup_rt_frame(int sig, struct ksignal *ksig, > err |= setup_sigcontext(&frame->uc.uc_mcontext, fp, regs, set->sig[0]); > err |= __copy_to_user(&frame->uc.uc_sigmask, set, sizeof(*set)); > > + if (!err) > + err = setup_sigcontext_ext(ksig, fp); > + Why is this not in setup_sigcontext, for example? > if (err) > return -EFAULT; > > @@ -576,6 +589,9 @@ static int x32_setup_rt_frame(struct ksignal *ksig, > regs, set->sig[0]); > err |= __copy_to_user(&frame->uc.uc_sigmask, set, sizeof(*set)); > > + if (!err) > + err = setup_sigcontext_ext(ksig, fpstate); > + > if (err) > return -EFAULT; > > @@ -707,6 +723,86 @@ setup_rt_frame(struct ksignal *ksig, struct pt_regs *regs) > } > } > > +#ifdef CONFIG_X86_64 > +static int copy_ext_from_user(struct sc_ext *ext, void __user *fpu) > +{ > + void __user *p; > + > + if (!fpu) > + return -EINVAL; > + > + p = fpu + fpu_user_xstate_size + FP_XSTATE_MAGIC2_SIZE; > + p = (void __user *)ALIGN((unsigned long)p, 8); > + > + if (!access_ok(VERIFY_READ, p, sizeof(*ext))) > + return -EFAULT; > + > + if (__copy_from_user(ext, p, sizeof(*ext))) > + return -EFAULT; > + > + if (ext->total_size != sizeof(*ext)) > + return -EINVAL; > + return 0; > +} > + > +static int copy_ext_to_user(void __user *fpu, struct sc_ext *ext) > +{ > + void __user *p; > + > + if (!fpu) > + return -EINVAL; > + > + if (ext->total_size != sizeof(*ext)) > + return -EINVAL; > + > + p = fpu + fpu_user_xstate_size + FP_XSTATE_MAGIC2_SIZE; > + p = (void __user *)ALIGN((unsigned long)p, 8); > + > + if (!access_ok(VERIFY_WRITE, p, sizeof(*ext))) > + return -EFAULT; > + > + if (__copy_to_user(p, ext, sizeof(*ext))) > + return -EFAULT; > + > + return 0; > +} > + > +int restore_sigcontext_ext(void __user *fp) > +{ > + int err = 0; > + > + if (boot_cpu_has(X86_FEATURE_SHSTK) && fp) { > + struct sc_ext ext = {0, 0}; > + > + err = copy_ext_from_user(&ext, fp); > + > + if (!err) > + err = cet_restore_signal(ext.ssp); > + } > + > + return err; > +} > + > +int setup_sigcontext_ext(struct ksignal *ksig, void __user *fp) > +{ > + int err = 0; > + > + if (boot_cpu_has(X86_FEATURE_SHSTK) && fp) { > + struct sc_ext ext = {0, 0}; > + unsigned long rstor; > + > + rstor = (unsigned long)ksig->ka.sa.sa_restorer; > + err = cet_setup_signal(is_ia32_frame(ksig), rstor, &ext.ssp); > + if (!err) { > + ext.total_size = sizeof(ext); > + err = copy_ext_to_user(fp, &ext); > + } > + } > + > + return err; > +} > +#endif > + > static void > handle_signal(struct ksignal *ksig, struct pt_regs *regs) > { > -- > 2.17.1 >
On Fri, Sep 21, 2018 at 5:09 PM Yu-cheng Yu <yu-cheng.yu@intel.com> wrote: > When setting up a signal, the kernel creates a shadow stack > restore token at the current SHSTK address and then stores the > token's address in the signal frame, right after the FPU state. > Before restoring a signal, the kernel verifies and then uses the > restore token to set the SHSTK pointer. [...] > +#ifdef CONFIG_X86_64 > +static int copy_ext_from_user(struct sc_ext *ext, void __user *fpu) > +{ > + void __user *p; > + > + if (!fpu) > + return -EINVAL; > + > + p = fpu + fpu_user_xstate_size + FP_XSTATE_MAGIC2_SIZE; > + p = (void __user *)ALIGN((unsigned long)p, 8); > + > + if (!access_ok(VERIFY_READ, p, sizeof(*ext))) > + return -EFAULT; > + > + if (__copy_from_user(ext, p, sizeof(*ext))) > + return -EFAULT; Why do you first manually call access_ok(), then call __copy_from_user() with the same size? Just use "if (copy_from_user(ext, p, sizeof(*ext)))" (without underscores) and get rid of the access_ok(). > + if (ext->total_size != sizeof(*ext)) > + return -EINVAL; > + return 0; > +} > + > +static int copy_ext_to_user(void __user *fpu, struct sc_ext *ext) > +{ > + void __user *p; > + > + if (!fpu) > + return -EINVAL; > + > + if (ext->total_size != sizeof(*ext)) > + return -EINVAL; > + > + p = fpu + fpu_user_xstate_size + FP_XSTATE_MAGIC2_SIZE; > + p = (void __user *)ALIGN((unsigned long)p, 8); > + > + if (!access_ok(VERIFY_WRITE, p, sizeof(*ext))) > + return -EFAULT; > + > + if (__copy_to_user(p, ext, sizeof(*ext))) > + return -EFAULT; Same as above. > + return 0; > +}
diff --git a/arch/x86/ia32/ia32_signal.c b/arch/x86/ia32/ia32_signal.c index 86b1341cba9a..cea28d2a946e 100644 --- a/arch/x86/ia32/ia32_signal.c +++ b/arch/x86/ia32/ia32_signal.c @@ -34,6 +34,7 @@ #include <asm/sigframe.h> #include <asm/sighandling.h> #include <asm/smap.h> +#include <asm/cet.h> /* * Do a signal return; undo the signal stack. @@ -108,6 +109,9 @@ static int ia32_restore_sigcontext(struct pt_regs *regs, err |= fpu__restore_sig(buf, 1); + if (!err) + err = restore_sigcontext_ext(buf); + force_iret(); return err; @@ -234,6 +238,10 @@ static void __user *get_sigframe(struct ksignal *ksig, struct pt_regs *regs, if (fpu->initialized) { unsigned long fx_aligned, math_size; + /* sigcontext extension */ + if (boot_cpu_has(X86_FEATURE_SHSTK)) + sp -= (sizeof(struct sc_ext) + 8); + sp = fpu__alloc_mathframe(sp, 1, &fx_aligned, &math_size); *fpstate = (struct _fpstate_32 __user *) sp; if (copy_fpstate_to_sigframe(*fpstate, (void __user *)fx_aligned, @@ -277,6 +285,8 @@ int ia32_setup_frame(int sig, struct ksignal *ksig, if (ia32_setup_sigcontext(&frame->sc, fpstate, regs, set->sig[0])) return -EFAULT; + if (setup_sigcontext_ext(ksig, fpstate)) + return -EFAULT; if (_COMPAT_NSIG_WORDS > 1) { if (__copy_to_user(frame->extramask, &set->sig[1], @@ -384,6 +394,9 @@ int ia32_setup_rt_frame(int sig, struct ksignal *ksig, regs, set->sig[0]); err |= __copy_to_user(&frame->uc.uc_sigmask, set, sizeof(*set)); + if (!err) + err = setup_sigcontext_ext(ksig, fpstate); + if (err) return -EFAULT; diff --git a/arch/x86/include/asm/cet.h b/arch/x86/include/asm/cet.h index ad278c520414..d9ae3d86cdd7 100644 --- a/arch/x86/include/asm/cet.h +++ b/arch/x86/include/asm/cet.h @@ -19,10 +19,15 @@ struct cet_status { int cet_setup_shstk(void); void cet_disable_shstk(void); void cet_disable_free_shstk(struct task_struct *p); +int cet_restore_signal(unsigned long ssp); +int cet_setup_signal(bool ia32, unsigned long rstor, unsigned long *new_ssp); #else static inline int cet_setup_shstk(void) { return 0; } static inline void cet_disable_shstk(void) {} static inline void cet_disable_free_shstk(struct task_struct *p) {} +static inline int cet_restore_signal(unsigned long ssp) { return 0; } +static inline int cet_setup_signal(bool ia32, unsigned long rstor, + unsigned long *new_ssp) { return 0; } #endif #endif /* __ASSEMBLY__ */ diff --git a/arch/x86/include/asm/sighandling.h b/arch/x86/include/asm/sighandling.h index bd26834724e5..23014b4082de 100644 --- a/arch/x86/include/asm/sighandling.h +++ b/arch/x86/include/asm/sighandling.h @@ -17,4 +17,9 @@ void signal_fault(struct pt_regs *regs, void __user *frame, char *where); int setup_sigcontext(struct sigcontext __user *sc, void __user *fpstate, struct pt_regs *regs, unsigned long mask); +#ifdef CONFIG_X86_64 +int setup_sigcontext_ext(struct ksignal *ksig, void __user *fpu); +int restore_sigcontext_ext(void __user *fpu); +#endif + #endif /* _ASM_X86_SIGHANDLING_H */ diff --git a/arch/x86/include/uapi/asm/sigcontext.h b/arch/x86/include/uapi/asm/sigcontext.h index 844d60eb1882..74f5ea5dcd24 100644 --- a/arch/x86/include/uapi/asm/sigcontext.h +++ b/arch/x86/include/uapi/asm/sigcontext.h @@ -196,6 +196,23 @@ struct _xstate { /* New processor state extensions go here: */ }; +#ifdef __x86_64__ +/* + * Sigcontext extension (struct sc_ext) is located after + * sigcontext->fpstate. Because currently only the shadow + * stack pointer is saved there and the shadow stack depends + * on XSAVES, we can find sc_ext from sigcontext->fpstate. + * + * The 64-bit fpstate has a size of fpu_user_xstate_size, plus + * FP_XSTATE_MAGIC2_SIZE when XSAVE* is used. The struct sc_ext + * is located at the end of sigcontext->fpstate, aligned to 8. + */ +struct sc_ext { + unsigned long total_size; + unsigned long ssp; +}; +#endif + /* * The 32-bit signal frame: */ diff --git a/arch/x86/kernel/cet.c b/arch/x86/kernel/cet.c index ec256ae27a31..5cc4be6e0982 100644 --- a/arch/x86/kernel/cet.c +++ b/arch/x86/kernel/cet.c @@ -18,6 +18,7 @@ #include <asm/fpu/types.h> #include <asm/compat.h> #include <asm/cet.h> +#include <asm/special_insns.h> static int set_shstk_ptr(unsigned long addr) { @@ -46,6 +47,69 @@ static unsigned long get_shstk_addr(void) return ptr; } +/* + * Verify the restore token at the address of 'ssp' is + * valid and then set shadow stack pointer according to the + * token. + */ +static int verify_rstor_token(bool ia32, unsigned long ssp, + unsigned long *new_ssp) +{ + unsigned long token; + + *new_ssp = 0; + + if (!IS_ALIGNED(ssp, 8)) + return -EINVAL; + + if (get_user(token, (unsigned long __user *)ssp)) + return -EFAULT; + + /* Is 64-bit mode flag correct? */ + if (ia32 && (token & 3) != 0) + return -EINVAL; + else if ((token & 3) != 1) + return -EINVAL; + + token &= ~(1UL); + + if ((!ia32 && !IS_ALIGNED(token, 8)) || !IS_ALIGNED(token, 4)) + return -EINVAL; + + if ((ALIGN_DOWN(token, 8) - 8) != ssp) + return -EINVAL; + + *new_ssp = token; + return 0; +} + +/* + * Create a restore token on the shadow stack. + * A token is always 8-byte and aligned to 8. + */ +static int create_rstor_token(bool ia32, unsigned long ssp, + unsigned long *new_ssp) +{ + unsigned long addr; + + *new_ssp = 0; + + if ((!ia32 && !IS_ALIGNED(ssp, 8)) || !IS_ALIGNED(ssp, 4)) + return -EINVAL; + + addr = ALIGN_DOWN(ssp, 8) - 8; + + /* Is the token for 64-bit? */ + if (!ia32) + ssp |= 1; + + if (write_user_shstk_64(addr, ssp)) + return -EFAULT; + + *new_ssp = addr; + return 0; +} + int cet_setup_shstk(void) { unsigned long addr, size; @@ -107,3 +171,54 @@ void cet_disable_free_shstk(struct task_struct *tsk) tsk->thread.cet.shstk_enabled = 0; } + +int cet_restore_signal(unsigned long ssp) +{ + unsigned long new_ssp; + int err; + + if (!current->thread.cet.shstk_enabled) + return 0; + + err = verify_rstor_token(in_ia32_syscall(), ssp, &new_ssp); + + if (err) + return err; + + return set_shstk_ptr(new_ssp); +} + +/* + * Setup the shadow stack for the signal handler: first, + * create a restore token to keep track of the current ssp, + * and then the return address of the signal handler. + */ +int cet_setup_signal(bool ia32, unsigned long rstor_addr, + unsigned long *new_ssp) +{ + unsigned long ssp; + int err; + + if (!current->thread.cet.shstk_enabled) + return 0; + + ssp = get_shstk_addr(); + err = create_rstor_token(ia32, ssp, new_ssp); + + if (err) + return err; + + if (ia32) { + ssp = *new_ssp - sizeof(u32); + err = write_user_shstk_32(ssp, (unsigned int)rstor_addr); + } else { + ssp = *new_ssp - sizeof(u64); + err = write_user_shstk_64(ssp, rstor_addr); + } + + if (err) + return err; + + set_shstk_ptr(ssp); + return 0; +} diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c index 92a3b312a53c..e9a85689143f 100644 --- a/arch/x86/kernel/signal.c +++ b/arch/x86/kernel/signal.c @@ -46,6 +46,7 @@ #include <asm/sigframe.h> #include <asm/signal.h> +#include <asm/cet.h> #define COPY(x) do { \ get_user_ex(regs->x, &sc->x); \ @@ -152,6 +153,10 @@ static int restore_sigcontext(struct pt_regs *regs, err |= fpu__restore_sig(buf, IS_ENABLED(CONFIG_X86_32)); +#ifdef CONFIG_X86_64 + err |= restore_sigcontext_ext(buf); +#endif + force_iret(); return err; @@ -266,6 +271,11 @@ get_sigframe(struct k_sigaction *ka, struct pt_regs *regs, size_t frame_size, } if (fpu->initialized) { +#ifdef CONFIG_X86_64 + /* sigcontext extension */ + if (boot_cpu_has(X86_FEATURE_SHSTK)) + sp -= sizeof(struct sc_ext) + 8; +#endif sp = fpu__alloc_mathframe(sp, IS_ENABLED(CONFIG_X86_32), &buf_fx, &math_size); *fpstate = (void __user *)sp; @@ -493,6 +503,9 @@ static int __setup_rt_frame(int sig, struct ksignal *ksig, err |= setup_sigcontext(&frame->uc.uc_mcontext, fp, regs, set->sig[0]); err |= __copy_to_user(&frame->uc.uc_sigmask, set, sizeof(*set)); + if (!err) + err = setup_sigcontext_ext(ksig, fp); + if (err) return -EFAULT; @@ -576,6 +589,9 @@ static int x32_setup_rt_frame(struct ksignal *ksig, regs, set->sig[0]); err |= __copy_to_user(&frame->uc.uc_sigmask, set, sizeof(*set)); + if (!err) + err = setup_sigcontext_ext(ksig, fpstate); + if (err) return -EFAULT; @@ -707,6 +723,86 @@ setup_rt_frame(struct ksignal *ksig, struct pt_regs *regs) } } +#ifdef CONFIG_X86_64 +static int copy_ext_from_user(struct sc_ext *ext, void __user *fpu) +{ + void __user *p; + + if (!fpu) + return -EINVAL; + + p = fpu + fpu_user_xstate_size + FP_XSTATE_MAGIC2_SIZE; + p = (void __user *)ALIGN((unsigned long)p, 8); + + if (!access_ok(VERIFY_READ, p, sizeof(*ext))) + return -EFAULT; + + if (__copy_from_user(ext, p, sizeof(*ext))) + return -EFAULT; + + if (ext->total_size != sizeof(*ext)) + return -EINVAL; + return 0; +} + +static int copy_ext_to_user(void __user *fpu, struct sc_ext *ext) +{ + void __user *p; + + if (!fpu) + return -EINVAL; + + if (ext->total_size != sizeof(*ext)) + return -EINVAL; + + p = fpu + fpu_user_xstate_size + FP_XSTATE_MAGIC2_SIZE; + p = (void __user *)ALIGN((unsigned long)p, 8); + + if (!access_ok(VERIFY_WRITE, p, sizeof(*ext))) + return -EFAULT; + + if (__copy_to_user(p, ext, sizeof(*ext))) + return -EFAULT; + + return 0; +} + +int restore_sigcontext_ext(void __user *fp) +{ + int err = 0; + + if (boot_cpu_has(X86_FEATURE_SHSTK) && fp) { + struct sc_ext ext = {0, 0}; + + err = copy_ext_from_user(&ext, fp); + + if (!err) + err = cet_restore_signal(ext.ssp); + } + + return err; +} + +int setup_sigcontext_ext(struct ksignal *ksig, void __user *fp) +{ + int err = 0; + + if (boot_cpu_has(X86_FEATURE_SHSTK) && fp) { + struct sc_ext ext = {0, 0}; + unsigned long rstor; + + rstor = (unsigned long)ksig->ka.sa.sa_restorer; + err = cet_setup_signal(is_ia32_frame(ksig), rstor, &ext.ssp); + if (!err) { + ext.total_size = sizeof(ext); + err = copy_ext_to_user(fp, &ext); + } + } + + return err; +} +#endif + static void handle_signal(struct ksignal *ksig, struct pt_regs *regs) {
When setting up a signal, the kernel creates a shadow stack restore token at the current SHSTK address and then stores the token's address in the signal frame, right after the FPU state. Before restoring a signal, the kernel verifies and then uses the restore token to set the SHSTK pointer. Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com> --- arch/x86/ia32/ia32_signal.c | 13 +++ arch/x86/include/asm/cet.h | 5 ++ arch/x86/include/asm/sighandling.h | 5 ++ arch/x86/include/uapi/asm/sigcontext.h | 17 ++++ arch/x86/kernel/cet.c | 115 +++++++++++++++++++++++++ arch/x86/kernel/signal.c | 96 +++++++++++++++++++++ 6 files changed, 251 insertions(+)